The present invention relates to an apparatus for optimizing or improving the rheological characteristics of viscous fluids.
It is a common practice in the oil and gas industry to produce viscous hydrocarbons from subsurface reservoirs using artificial lift methods. These methods relate mainly to pumping devices such as centrifugal, positive displacement or progressive cavity type of pumps. In some reservoirs producing high viscosity hydrocarbons, the natural reservoir energy is sufficient to allow the fluids to flow unaided to the surface. However, there are very few reservoirs where this is the case. This is due to the very high friction losses created by the particular Theological properties of the fluids. It is therefore necessary to overcome such losses using artificial means like pumps, in order to make exploitation of the hydrocarbons economically viable.
Devices such as pumps required a source of energy to be operated. In most cases, either mechanical or electrical energy is transmitted to the pump in order to produce fluids. Therefore, continuous production of viscous hydrocarbons requires a significant amount of energy, mainly electricity. In addition, a pump system breakdown require that the unit is removed from the well and replaced. The overall cycle of installing the pumps, producing the fluids and replacing the pump units after failure is time consuming and expensive. However, the most costly part is the production phase which requires very high levels of continuous energy in order to produce the fluids. Most of this energy is dissipated as friction losses either in the pump or in the piping system transporting the fluids to the surface.
Mechanical and magnetic treatment of fluids has been carried out in various industries over the last 25 years. In the case of magnetic energy, the main effect on the fluid has been to add energy to the atomic levels of the fluid. Scale deposition in pipes and surfaces can be inhibited with this process in which the energy added to the fluid by the magnetic field will increase the magnitude of the atoms""s repulsion forces that hold the scale particles in suspension (U.S. Pat. No. 4,357,2347). Hydrocarbons can be treated using magnetic fields in order to prevent wax and paraffin deposition in pipes and surfaces (U.S. Pat. Nos. 5,454,943; 5,052,491; 5,024,271; 4,033,151). Magnetized fluids are also used in applications where the viscosity of the fluid needs to be controlled, they are normally composed of suspensions of micron-sized, magnetizable particles in a medium such as water or oil. European Patent EP 317186 represents this application for cooling fluids in motor cars in which the viscosity of the fluid is varied depending on the temperature and engine speed. EP 726193 presents a similar application where a magnetized fluid is subjected to a magnetic field which varies its viscosity, hence reducing the resistance to move between the two pieces. None of the inventions described above addresses the combined effect of mechanical and magnetic energy for the sole purpose of modifying the viscosity of viscous fluids (mainly hydrocarbons) deep in the underground wells and reservoirs.
It is an object of the present invention to provide a new and improved apparatus for the optimization of the rheological characteristics of viscous fluids such as hydrocarbons, such that less power is required to pump such fluids from a subsurface reservoir to the surface.
According to the present invention, an apparatus for optimizing the rheological properties of a viscous fluid is provided, which comprises a housing having a through bore defining a cross-sectional flow area for fluid through the bore, the through bore having an inlet end for connection to a supply of a viscous fluid and an outlet end, a flow restriction device in the through bore defining a reduced area orifice for restricted flow, and an adjustment device for varying the size of the orifice. A magnetic field source may be selectively secured to the housing for generating a magnetic field across at least part of the through bore.
The housing is designed to be lowered into a well and connected in line with production tubulars linking a subsurface reservoir to the surface. The housing is suitably placed close to the junction between the reservoir and the flow path or tubulars connecting the reservoir to the surface.
In an exemplary embodiment, one or more magnetic units are provided for selectively securing to the housing to generate an adjustable magnetic field for fluids which are sensitive to both shear and magnetic field. However, for fluids which are not sensitive to shear, the magnetic field source may be used alone, and the flow restriction device may be used independently for fluids not sensitive to magnetic fields.
In one embodiment of the invention, the magnetic unit comprises at least one sleeve releasably secured in the through bore at one end of the housing, and contains one or more permanent magnets. Alternatively, sleeves providing a magnetic field may be releasably secured in both ends of the bore, with the flow restriction device located between the two sleeves.
The housing is designed to be mounted in a production line for fluid such as hydrocarbons from a subsurface reservoir, such that reservoir fluids are induced to flow through the housing to the surface. Optimization or conditioning of the rheological characteristics, or viscosity, is accomplished by the action of the magnetic field and/or the acceleration of the fluid across the small flow area orifice where shearing takes place. The time and magnitude of both the mechanical action provided by the flow restriction device, and the magnetic field acting on the fluid, will be determined by the characteristics of the fluid, reservoir, and the well.
The apparatus is capable of substantially reducing the viscosity of a fluid to levels where significant energy savings are realized. As a result, wells such as oil wells with pumps will require much less energy to pump the oil to the surface. In some cases, pumps or other artificial lift means may not even be needed, making the economics of installing and running the wells much more attractive.